Background: It is well established that the presence of bacteria in the intestine has a profound influence on health. Probiotics, ("beneficial bacteria") have shown ameliorating effects on various infectious diseases. The influence of probiotics on several immune-mediated conditions has also been investigated, among them, atopic dermatitis ("Asthma of the skin"), and milk allergy.

The precise mechanism of action of probiotics is not fully understood. Several animal and human studies have shown the probiotic bacteria to influence the immune system. The aim of the present study is to evaluate whether supplementing the diet with oral probiotics affects the immune response of children following routine vaccination against 4 common childhood viral diseases: Mumps, Measles, Rubella and Varicella.

Objective(s) and Hypothesis(es):

Hypothesis: Administration of probiotics will increase the amount of antibodies produced following vaccination for Measles, Mumps, Rubella and Varicella, by over 15%.

Objectives:

• To determine whether administration of probiotics during infancy influences antibody levels following the routine childhood vaccinations.
• To determine whether administration of probiotics during infancy influences the rate of adverse effects following the routine childhood vaccinations.

Potential Impact: Vaccines, alongside with the discovery of Penicillin, have been cited as the great public health successes of the 20th century. However, even in countries with maximal childhood immunization coverage, the protective effect is not optimal. For example, only 70% to 90% of children immunized against chickenpox are actually protected against the disease. If we succeed in raising these numbers, even by a single percent, it will have a huge impact on society.

Inclusion Criteria:

• Age: 9-11 months.
• Parent or guardian intending to follow the recommended immunization schedule in Israel.
• Parent or guardian possessing sufficient knowledge of the Hebrew language.

Exclusion Criteria:

• Infants suffering from any chronic diseases / conditions resulting in immune depression.
• Infants taking medications affecting the immune system.
• Infants with permanent invasive catheters.
• Infants born prematurely (prior to gestational week 35)
• Parent or guardian objecting to collection of blood sample at the end of study.